The need to prevent childhood obesity extends down to our youngest children. Obesity and excessive weight gain in the first few years of life are independently associated with higher blood pressure, recurrent wheezing, higher hospital admission rates, and other adverse physical and psychosocial health conditions in childhood. Thus, effective approaches to prevent obesity in early childhood are needed. Because nearly two-thirds of U.S. children under six years of age are routinely cared for outside of the home, organized child care is an important setting for obesity prevention. Few interventions, however, have focused on child care, and even fewer have targeted very young children in care. The proposed study is a novel intervention targeting both the environment of the child care center, the family home, and the interactions that take place between children and their care providers. The primary aim of this study is to evaluate the efficacy of a six-month-long intervention in improving the nutrition and physical activity environments of child care centers serving racially and ethnically diverse children from birth to two years of age and the family home. The study will be a randomized controlled trial with 640 children attending 80 child care centers in North Carolina. The focus will be on center policies, provider and parent practices, and children's home environments that influence dietary intake and physical activity. The intervention will include four complementary and mutually reinforcing components: (1) center self-assessment; (2) targeted technical assistance and guidance by a health professional for providers and parents; (3) training for child care providers; and (4) parent outreach and support. Centers randomized to the control arm will receive intervention materials and abbreviated technical assistance at the end of the intervention. Outcomes for this study include child dietary intake, physical activity, and two adiposity measures: weight-for-length and skin fold thicknesses. Child care centers and children's home environments will also be measured to evaluate how well they support healthy behaviors. Results of this study will provide new information on nutrition and physical activity policies and practices within child care centers and the family home. Findings will also inform policy efforts to improve the child care system and help prevent obesity in very young children.